Which type of switch is connected between two 3-way switches and does not have "ON" and "OFF" markings?

The correct answer is the 4-way switch, as it is specifically designed to be used in a circuit that contains two 3-way switches. A 4-way switch allows you to control a light or appliance from three or more locations by providing additional switching options between two 3-way switches.

Unlike single-pole or double-pole switches that are typically used in basic configurations where there's a clear "ON" and "OFF" state, the 4-way switch does not have these markings because its function is to switch the circuit's path based on the positions of the attached 3-way switches. This makes its operation dependent on the other switches in the circuit rather than relying on a simple on/off mechanism.

The 3-way switch, on the other hand, can control a light from two locations but will have "ON" and "OFF" markings to reflect its function. Similarly, single-pole and double-pole switches serve different roles in electrical wiring and are not suitable for the configuration required between the two 3-way switches in this scenario. Thus, the 4-way switch is the component that fits perfectly into this configuration without "ON" and "OFF" markings.